1. Field of the Invention
The present invention relates to an encoder for detecting position or angle information, which is employed for an industrial measurement machine and the like.
2. Related Background Art
Up to now, the applicant of the present invention has proposed a so-called grating interference type encoder that detects variations in position and velocity of an object by utilizing a light diffraction interference phenomenon. In particular, there has been proposed an encoder having a far higher resolution than a geometrical optical encoder, which is obtained in the case where a minute scale of the micron order is used and two of light fluxes diffracted by the scale are taken out to interfere with each other (Japanese Patent Application Laid-Open No. 2001-336952 or the like). Those encoders have a structure in which the wave fronts of the two diffraction light fluxes are synthesized to produce an interference pattern. However, because the encoders are of an interference optical system, it is very hard to process respective optical elements and to improve alignment accuracy thereof under the current circumstances. In particular, in the case of a so-called built-in type encoder having a scale section and a detection head section which are separately provided, the user him/herself has to attach the scale section and the detection head section to a motor, a stage, and the like. Therefore, a problem arises in that the alignment operation becomes complicated. In addition, in the case where the scale section and the detection head section are attached to an actual device, it is desired to further reduce the sizes thereof.
Also, in order to realize higher accurate measurement control, an origin position measurement with reproducibility becomes important. Up to now, it is general that an additional origin detecting sensor is provided somewhere to a rotary mechanism connected with the rotational axis of the grating interference type encoder to ensure the measurement reproducibility.
However, according to the conventional technique, the high-precision grating interference type encoder and the origin detecting sensor provided to the mechanism are separately provided. Thus, it is difficult to sufficiently ensure the measurement reproducibility because of rigidity of the connected mechanism and an Abbe error. Therefore, there are drawbacks concerning size reduction of an applied device and incorporation and adjustment operation of an encoder. As counter measures capable of solving the above-mentioned drawbacks, the applicant of the present invention has proposed a technique for reducing the influence of an alignment error and various grating interference type encoders that provide an origin detection output in addition to an encoder output by producing an origin detection pattern in the vicinity of a grating to be measured of a grating interference type encoder.
However, in order to pursue a downsized and higher precision detecting sensor or encoder, and an improved easiness of its incorporation, further technical improvements have been required.